Nature provides the means for the sustainable management of floods

22.03.2018

World Water Day is held on 22 March. This year's theme is "Nature for water", which highlights how natural methods can be used in curbing flooding, droughts and water pollution.

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Climate change is expected to alter the annual distribution of rainfall, which means that floods during the growth period may become more common. Vegetation had a great impact on the levels to which flood waters rose during the Vantaanjoki river's summer floods in 2004. Photo: Juha Järvelä

Soon, spring and the melting snow will yet again be visible as flooding around Finland. Although major floods caused by extreme weather phenomena are rare in the Nordic countries, floods cause financial loses even here each year. Climate change is expected to increase flooding in the future.

In relation, human activities affect the water cycle of the built environment more profoundly than weather phenomena or climate change do, Aalto University researchers say.

Thinking that we are the victims of climate change or heavy rainfalls is a poor approach. We have caused many problems - and we can also resolve these,' says postdoctoral researcher Nora Sillanpää from the Aalto University School of Engineering, who researches urban drainage.

For example, as urban areas are increasingly covered in asphalt, this prevents rain and melt water from evaporating naturally and their infiltration into the soil. This will mean that storm water flows into natural water courses and intensifies flooding.

'Floods have traditionally been managed with methods that are harmful to the environment and unsustainable,' Sillanpää says.

An effort is being made to manage urban storm water floods, for example, by building detention ponds to which storm water is directed. The detention ponds may shift flooding issues to natural waterways

Generally, the ponds manage the symptom without tackling the problem - the fact that large runoff volumes accumulate in cities. Contaminants flow with runoff into natural bodies of water.

Researchers at Aalto University are looking into decentralised methods that can promote a more natural water cycle also in urban areas.

'In this case, natural does not mean that the solutions come about by themselves, on the contrary, they will require complex technology and engineering expertise,' says Sillanpää.

Sillanpää uses the environment around supermarkets as an example. A natural water cycle could be promoted by building a green roof that would promote the evaporation of water. Permeable surfaces could be built between parking spots, ensuring that rain water could be infiltrated by the soil.

According to Sillanpää, water should not only be seen as a problem, but also as a resource.

'Instead of washing cars, flushing toilets and irrigating plants with water that is suitable for drinking, we could utilise rain water.'

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Storm waters can also be utilised as part of the urban environment's image.  'This makes the urban environment more interesting and increases the value of real estate,' Nora Sillanpää says. Photo: Nora Sillanpää

Floodplains can reduce pollution in natural water bodies

Aalto University researchers have also examined environmentally-friendly solutions for flood management in agricultural areas.

The drainage of agricultural lands intensifies flooding as excess waters from fields and forests drain into streams and rivers. In Southern Finland, only 2-7 percent of the total length of streams are in their natural state or in a natural-like state.

Flooding has traditionally been managed by making the streams wider and straighter and by stripping away their natural vegetation. These channelization measures will have a negative effect on fish populations in rivers and streams as well as on nature's own water purification processes. When vegetation that retains solids, nutrients and contaminants is removed, these substances will drift directly from fields into inland water bodies and the sea.

'Substances that pollute the Baltic Sea flow into it via small agricultural streams. However, we have the ability to influence small streams,' says Kaisa Västilä, a postdoctoral researcher at the Aalto University School of Engineering.

Västilä has conducted unique research in Finland on the use of two-stage drainage channels as a method for flood management. In the case of a two-level drainage channel, the natural channel is not dug open as was traditionally done. Instead, a floodplain is built on one or both sides of the channel. This makes it possible to save the channel's natural ecosystem.

Floodplains allow the controlled use of vegetation that collects solids from the catchment areas and takes up excess nutrients from the water.

'The two-stage method utilises these natural purification processes, but with added research data and engineering expertise,' Västilä sums up.

A two-stage channel with a floodplain is also becoming more common as an alternative for the environmentally-harmful channelization of urban streams.

'A more environmentally-friendly way to manage floods will require more extensive planning. We will need more research-based information that can be exported to designers' desks,' says Västilä.

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A floodplain when water level is low. Vegetation binds solids, nutrients and contaminants and prevents them from being transported into downstream water bodies. Photo: Juha Järvelä

Flood management requires multidisciplinary research data

Floods are complex phenomena. In order to be able to understand and manage them, we will need multidisciplinary research and diverse research methods.

The strength of Aalto University's Water and Environmental Engineering research lies in the ability to utilise computational models, field research and tests conducted in laboratory facilities.

'We can then select from these the most suitable tool at any given time. All of these are needed as they support one another and create a comprehensive overall picture,' says Juha Järvelä, a researcher and teacher of natural water hydraulics and environmentally friendly water construction.

Aalto University has a unique research environment by Finnish standards: A 20-metre-long water flume that is like an indoors river. It can be used to examine such things as the impact vegetation has on the flow of water and the transport of substances. The information gained from this research will help in the design of more reliable flood models and in finding environmentally-sustainable ways to manage vegetation in rivers.

'Aalto's strength lies in a solution-based approach and strong connection to practice. We do not focus on just identifying problems, but on developing genuine solutions to these,' Järvelä says.

Research is carried out in close cooperation with cities, designers, authorities and businesses - i.e. those who need and use this information.

'Urbanisation is a worldwide megatrend. The solutions developed here can also utilised in the world's massive metropolises,' points out Professor Harri Koivusalo from the Aalto University School of Engineering.

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The role of vegetation in the occurrence of waterway flooding and the level flood waters rise will be emphasised as climate change continues. The impact of vegetation is researched at Aalto University with a 20-metre-long water flume. Photo: Mikko Raskinen

Climate change and urbanisation make more effective flood management a necessity

The importance of flood management will be increasingly highlighted in the future as the climate changes and the built environment expands and becomes more densely built.

'Floods are natural phenomena with which we must learn to live. We have to focus on how we can live with them in as smart a way as possible,' Juha Järvelä explains.

However, this does not mean that we have to raise our hands in defeat. The effects of climate change can be effectively compensated for with research data-based land use planning and construction.

'We need bold solutions for increasingly densely built urban areas. We need to adopt a completely new way of thought in how to build cities,' explains Nora Sillanpää.

'However, we must develop all areas in the light of the best research data and sustainable principles. We have room for improvement in this respect.'

More information:

Postdoctoral researcher Nora Sillanpää
Tel. +358 50 386 3325
nora.sillanpaa@aalto.fi

Postdoctoral researcher Kaisa Västilä
Tel. +358 50 408 1390
kaisa.vastila@aalto.fi

Professor Harri Koivusalo
Tel. +358 50 570 9864
harri.koivusalo@aalto.fi